Unfortunately there is no standardization.The exact values sometimes noticably differ among the various Unix flavours.

Some examples for such values:

"C" - the standard value, usually the default, the same like not setting the category at all. 7-bit ASCII charset, no goodies. Ironically enough, at least one vendor (HP) apparently felt the need to provide "C.iso88591". The name C is associated with ANSI C.

"en_US, en_US.iso88591" - ascii and the western europe specific characters.en_US (if available) always contains iso8859-1, even without the codeset suffix.

However HP-UX 10/11 provide only values with the codeset, for example en_US.iso88591. You see it's essential to find out about the valid values instead of only guessing.

although "de_DE" is valid syntax, this value doesn't exist on many Solaris versions (but only "de").

"fr_CA.roman8" - might be appropriate for canadians

"zh_TW.big5" traditional chinese in taiwan with the BIG5 codeset (not an eight bit locale, but a good example).

"en_US.ISO8859-15@euro" - example from Solaris supporting the "euro sign" instead of the dollar sign as currency character (apart from that @euro is the default for iso8859-15).